Laser marking in packages

ABSTRACT

A package includes a device die, a first plurality of redistribution lines underlying the device die, a second plurality of redistribution lines overlying the device die, and a metal pad in a same metal layer as the second plurality of redistribution lines. A laser mark is in a dielectric layer that is overlying the metal pad. The laser mark overlaps the metal pad.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No. 14/192,341, entitled “Laser Marking in Packages,” filed on Feb. 27, 2014, which application is incorporated herein by reference.

BACKGROUND

In the packaging of integrated circuits, there are various types of packaging methods and structures. For example, in a conventional Package-on-Package (POP) process, a top package is bonded to a bottom package. The top package and the bottom package may also have device dies packaged therein. By adopting the PoP process, the integration level of the packages is increased.

In an existing PoP process, the bottom package is formed first, which includes a device die bonded to a package substrate. A molding compound is molded on the package substrate, wherein the device die is molded in the molding compound. The package substrate further includes solder balls formed thereon, wherein the solder balls and the device die are on a same side of the package substrate. The solder balls are used for connecting the top package to the bottom package.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1 through 5 illustrate the cross-sectional views of intermediate stages in the formation of a package in accordance with some embodiments;

FIG. 6 illustrates a top view of a package in accordance with some embodiments, wherein a laser mark and a respective metal pad are formed overlapping a device die in the package; and

FIG. 7 illustrates a top view of a package in accordance with some embodiments, wherein a laser mark and a respective metal pad are misaligned with device dies in the package.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,” “lower,” “overlying,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

A package and the method of forming laser marks in the package are provided in accordance with various exemplary embodiments. The variations of the embodiments are discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

FIG. 1 illustrates a cross-sectional view of package 100. In some embodiments, package 100 includes device die 102, with the front side of device die 102 facing down and bonded to Redistribution Lines (RDLs) 112. In alternative embodiments, package 100 includes more than one device die. Device die 102 may include semiconductor substrate 108, and integrated circuit devices 104 (such as active devices, which include transistors, for example) at the front surface (the surface facing down) of semiconductor substrate 108. Device die 102 may include a logic die such as a Central Processing Unit (CPU) die, a Graphic Processing Unit (GPU) die, a mobile application die, or the like.

Device die 102 is molded in molding material 120, which surrounds device die 102. Molding material 120 may be a molding compound, a molding underfill, a resin, or the like. The bottom surface 120A of molding material 120 may be leveled with the bottom ends of device dies 102. The top surface 120B of molding material 120 may be level with or higher than back surface 108A of semiconductor substrate 108. In some embodiments, back surface 108A of semiconductor substrate 108 is overlapped by die-attach film 110, which is a dielectric film adhering device die 102 to the overlying dielectric layer 118. Device die 102 further includes metal pillars/pads 106 (which may include copper pillars, for example) in contact with, and bonded to, RDLs 112.

Package 100 may include bottom-side RDLs 112 underlying device die 102, and top-side RDLs 116 overlying device dies 102. Bottom-side RDLs 112 are formed in dielectric layers 114, and top-side RDLs 116 are formed in dielectric layers 118. RDLs 112 and 116 may be formed of copper, aluminum, nickel, titanium, alloys thereof, or multi-layers thereof. In some embodiments, dielectric layers 114 and 118 are formed of organic materials such as polymers, which may further include polybenzoxazole (PBO), benzocyclobutene (BCB), polyimide, or the like. In alternative embodiments, dielectric layers 114 and 118 are formed of inorganic material such as silicon oxide, silicon nitride, silicon oxynitride, or the like.

Through-Vias 122 are formed to penetrate through molding material 120. In some embodiments, through-vias 122 have top surfaces level with the top surface 120B of molding material 120, and bottom surfaces level with the bottom surface 120A of molding material 120. Through-Vias 122 electrically connect bottom-side RDLs 112 to top-side RDLs 116. Through-Vias 122 may also be in physical contact with bottom-side RDLs 112 and top-side RDLs 116.

Electrical connectors 124, which are formed of a non-solder metallic material(s), are formed at the bottom surface of package 100. In some embodiments, electrical connectors 124 include Under-Bump Metallurgies or metal pads. In alternative embodiments, electrical connectors 124 include metal pillars such as copper pillars. Throughout the description, electrical connectors 124 are referred to as metal pads 124, although they may have other forms. In accordance with some embodiments, metal pads 124 comprise copper, aluminum, titanium, nickel, palladium, gold, or multi-layers thereof. In some embodiments, as shown in FIG. 1, the bottom surfaces of metal pads 124 are level with the bottom surface of the bottom dielectric layer 114. In alternative embodiments, the bottom surfaces of metal pads 124 extend below the bottom surface of the bottom dielectric layer 114. In some embodiments, solder regions 126 are attached to the bottom surfaces of metal pads 124.

Metal pad 128 is formed in one of metal layers in which RDLs 116 are formed. In some embodiments, metal pad 128 is electrically floating. In alternative embodiments, metal pad 128 is electrically connected to other conductive features such as RDLs 116 and/or through-vias 122. For example, metal pad 128 may be connected to the electrical ground. Metal pad 128 is formed simultaneously when the respective RDLs 116 in the same metal layer are formed.

In some exemplary embodiments, seal ring 130 is formed to encircle metal pad 128, wherein the exemplary seal ring 130 may be found in FIGS. 6 and 7. As shown in FIG. 1, seal ring 130 is formed in the same metal layer as metal pad 128. In some embodiments, seal ring 130 is electrically floating, and may be fully enclosed by dielectric materials. In alternative embodiments, seal ring 130 is electrically coupled to other conductive features such as RDLs 116 and/or through-vias 122. Seal ring 130 is formed simultaneously when metal pad 128 is formed. In alternative embodiments, no seal ring is formed to encircle metal pad 128.

In accordance with some embodiments, the bottom surfaces of metal pad 128 and seal ring 130 are higher than the top surface of die-attach film 110 and the top surface 120B of molding material 120. One of dielectric layers 118 is formed underneath metal pad 128 and seal ring 130, with the top surface of the respective dielectric layer 118 contacting the bottom surfaces of metal pad 128 and seal ring 130. Overlying metal pad 128 and seal ring 130, there exists an additional layer, which is one of dielectric layers 118, and is marked as 118′.

Referring to FIG. 2, a laser marking is performed to form laser marks 132 in dielectric layer 118′, wherein laser marks 132 include the trenches formed in dielectric layer 118′. The laser marking is performed using laser beam 134, which burns and removes parts of dielectric layer 118′. The burned parts of dielectric layer 118′ overlap metal pad 128. Metal pad 128 acts as a protection layer, wherein laser beam 134 is not able to penetrate through metal pad 128. Hence, metal pad 128 has the function of preventing laser beam 134 from reaching the underlying device die 102 and the underlying RDLs 116, if any. After the laser marking, some portions of metal pads 128 are exposed through the trenches that form laser marks 132. Laser marks 132 may include letters, digits, figures, or any other symbols that can be used for identification purpose. For example, FIGS. 6 and 7 illustrate some exemplary laser marks 134 that include letters and digits. Laser marks 132 may be used to identify the product, the manufacturing sequence, or any other information that is used to track the respective package.

FIG. 3 illustrates the removal of some parts of dielectric layers 118 to expose metal pads 116′, which may be parts of RDLs 116. As a result, openings 136 are formed in dielectric layers 118′. The formation of openings 136 may be achieved through laser burning. Alternatively, when dielectric layer 118′ is formed of a light-sensitive material such as PBO or polyimide, the formation of openings 136 may be achieved through a light-exposure followed by a development step.

FIG. 4 illustrates the formation of solder balls 138. In some embodiments, a ball placement step is performed to drop solder balls in openings 136 (FIG. 3), followed by a reflow process to reflow the solder balls. In alternative embodiments, no solder ball is applied in openings 136. Rather, the solder is in package 200 as in FIG. 5.

FIG. 5 illustrates the bonding of package 200 with package 100. In some embodiments, package 200 includes package substrate 202, and device die(s) 204 bonded to package substrate 202. The bonding of device dies 204 to package substrate 202 may be achieved through wire bonding, flip-chip bonding, or the like. Solder regions 138 as shown in FIG. 4 are reflowed to bond package 200 to package 100. In some embodiments, after the bonding of package 200, underfill 140 is filled into the gap between package 100 and package 200. In these embodiments, the trenches of laser mark 132 (FIG. 4) are also filled with underfill 140. Accordingly, the portions of underfill 140 in the trenches of the laser mark 132 are referred to as laser marks 132′. Laser marks 132′ may extend from the top surface of dielectric layer 118′ to the top surface of metal pad 128. Furthermore, laser marks 132′ may be in physical contact with the top surface of metal pad 128.

In the package as shown in FIG. 5, metal pad 128 may be fully enclosed by, and in contact with, dielectric materials including dielectric layers 118 and underfill 140. In alternative embodiments, no underfill is filled into the gap between package 100 and package 200, and laser marks 132 remain to be air gaps. In these embodiments, some portions of metal pad 128 may be exposed to air through laser marks 132.

FIG. 6 illustrates a top view of package 100 in accordance with some embodiments. As shown in FIG. 6, laser marks 132 are formed to overlap metal pad 128, wherein all laser marks 132 are formed on metal pad 128 or other metal pads. Seal ring 130 is formed in some embodiments, and forms a ring encircling metal pad 128. In some exemplary embodiments, the length L1 and width W1 of metal pad 128 are greater than about 2 cm to allow an adequate area for forming laser marks 132. Seal ring 130 is formed to prevent the heat generated during the laser marking from being propagated to other regions.

During the laser marking, heat is generated, and may damage the structures including RDLs and dielectric layers. To reduce or at least eliminate the damage caused by the heat, seal ring 130 may have a greater width W2, for example, greater than about 20 μm to provide a low thermal resistivity, so that an overheated portion of seal ring 130 may quickly dissipate the heat to other portions of seal ring 130. In alternative embodiments, no seal ring 130 is formed.

In the embodiments as shown in FIG. 6, through-vias 122 may be formed close to the peripheral of package 100, although through-vias 122 may also be formed in any other locations of package 100. Through-vias 122 may be aligned to a ring that encircles metal pad 128 in some embodiments.

In FIG. 6, metal pad 128 and laser marks 132 are formed directly over, and overlap, die 102. In alternative embodiments, as shown in FIG. 7, which also illustrates a top view of package 100, metal pad 128 and laser marks 132 are not aligned to device die 102. This embodiment may be used when there is enough space for allocating metal pad 128.

The embodiments of the present disclosure have several advantageous features. By forming metal pads, the device dies and the redistribution lines in the packages are protected from the likely damage caused by the laser marking. The embodiments of the present disclosure do not incur additional manufacturing cost since the metal pads may be formed at the same time the redistribution lines of the package are formed.

In accordance with some embodiments of the present disclosure, a package includes a device die, a first plurality of redistribution lines underlying the device die, a second plurality of redistribution lines overlying the device die, and a metal pad in a same metal layer as the second plurality of redistribution lines. A laser mark is in a dielectric layer that is overlying the metal pad. The laser mark overlaps the metal pad.

In accordance with alternative embodiments of the present disclosure, a first package includes at least one first dielectric layer, a first plurality of redistribution lines in the at least one first dielectric layer, a device die over and electrically coupled to the first plurality of redistribution lines, a molding material molding the device die therein, a through-via penetrating through the molding material, at least one second dielectric layer over the device die, and a second plurality of redistribution lines in the at least one second dielectric layer. The second plurality of redistribution lines is electrically coupled to the first plurality of redistribution lines through the through-via. The first package further includes a metal pad in the at least one second dielectric layer, a third dielectric layer overlying the at least one second dielectric layer, and a laser mark extending from a top surface of the third dielectric layer to a top surface of the metal pad. A second package is over the first package, wherein the second package is bonded to the first package.

In accordance with yet alternative embodiments of the present disclosure, a method includes performing a laser marking on a package. The package includes at least one first dielectric layer, a first plurality of redistribution lines in the at least one first dielectric layer, a device die over and electrically coupled to the first plurality of redistribution lines, a molding material molding the device die therein, a through-via penetrating through the molding material, at least one second dielectric layer over the device die, a second plurality of redistribution lines in the at least one second dielectric layer, wherein the second plurality of redistribution lines is electrically coupled to the first plurality of redistribution lines through the through-via, a metal pad in the at least one second dielectric layer. The package further includes a third dielectric layer overlying the at least one second dielectric layer. The laser marking forms a laser mark in the third dielectric layer, with portions of the metal pad exposed to the laser mark.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method comprising: forming a first package comprises: at least one first dielectric layer; a first plurality of redistribution lines in the at least one first dielectric layer; a device die over and electrically coupled to the first plurality of redistribution lines; a molding material molding the device die therein; a through-via penetrating through the molding material; at least one second dielectric layer over the device die; a second plurality of redistribution lines in the at least one second dielectric layer; and a metal pad in the at least one second dielectric layer; and performing a laser marking to form a laser mark in a third dielectric layer over the metal pad, wherein a portion of the metal pad is exposed to the laser mark.
 2. The method of claim 1 further comprising: forming openings in the third dielectric layer to expose a plurality of metal pads; disposing solder regions in the openings; and performing a reflow on the solder regions to connect the solder regions with the plurality of metal pads.
 3. The method of claim 1 further comprising: bonding a second package to the first package; and filling an underfill into a gap between the first package and the second package, wherein the underfill is disposed into the laser mark.
 4. The method of claim 3, wherein the underfill is in physical contact with the metal pad.
 5. The method of claim 1, wherein the metal pad stops a laser beam used in the laser marking.
 6. The method of claim 1 further comprising, when the metal pad is formed, simultaneously forming a seal ring encircling the metal pad.
 7. The method of claim 1 further comprising forming a redistribution line in the at least one second dielectric layer, with the redistribution line electrically connecting the metal pad to the through-via.
 8. The method of claim 1 further comprising electrically grounding the metal pad.
 9. The method of claim 1, wherein the metal pad is electrically floating.
 10. A method comprising: forming a first package comprising: forming a Redistribution Line (RDL) and a metal pad simultaneously, wherein the RDL and the metal pad are over a device die and an encapsulating material, and the device die is encapsulated by the encapsulating material; and performing a laser drilling on a dielectric layer covering the RDL and the metal pad to form an opening and a laser mark, respectively, wherein the laser mark comprises information for identifying the first package; bonding a second package to the first package through a solder region disposed in the opening in the dielectric layer; and filling the laser mark with an underfill.
 11. The method of claim 10 further comprising, during the laser marking, conducting heat generated by the laser drilling to a through-via in the encapsulating material through an additional RDL electrically coupling the metal pad to the through-via.
 12. The method of claim 10 further comprising, during the laser marking, conducting heat generated by the laser drilling to a metal seal ring encircling the metal pad.
 13. The method of claim 12, wherein the metal pad and the metal seal ring are in a same metal layer.
 14. The method of claim 10, wherein the laser mark comprises a letter, a digit, or combinations thereof.
 15. The method of claim 10, wherein the metal pad is exposed through the laser mark.
 16. A method comprising: forming a first package comprising: encapsulating a device die and a through-via in an encapsulating material; forming a plurality of dielectric layers over the device die, the through-via, and the encapsulating material; forming a Redistribution Line (RDL) and a metal pad in the plurality of dielectric layers; and performing a laser drilling on a top dielectric layer in the plurality of dielectric layers to form an opening and a laser mark, with the RDL and the metal pad being exposed through the opening and the laser mark, respectively, wherein the top dielectric layer covers the RDL and the metal pad; filling a solder region into the opening to contact the RDL; and filling a dielectric material into the laser mark to contact the metal pad.
 17. The method of claim 16 further comprising: bonding a second package to the first package through the solder region; and disposing an underfill into a gap between the first package and the second package, wherein the dielectric material filling the laser mark is a part of the underfill.
 18. The method of claim 16, wherein the metal pad is fully enclosed in dielectric materials.
 19. The method of claim 16 further comprising, during the laser marking, conducting heat generated by the laser drilling to the through-via through a heat path, with an entirety of the heat path being formed of metal.
 20. The method of claim 16 further comprising, during the laser marking, conducting heat generated by the laser mark to a metal seal ring encircling the metal pad, wherein the metal seal ring is separated from the metal pad by a dielectric material, and no additional metal feature is between the metal pad and the metal seal ring. 